Dual acceleration range integrating accelerometer



April 6, 1955 H. D. MoRRls ETAL 3,176,518

DUAL ACCELERATION RANGE INTEGRATING ACCELEROMETER Filed Aug. 24, 1961 2Sheets-Sheet 1 INVENTORS #ara /d Mor/7.5. BY h/a//ace E. Hyde, ./f:

April 6, 1965 H. D. MORRIS ETAL 3,176,513

DUAL ACCELERATION RANGE INTEGRATING ACCELROMETER Filed Aug. 24. 1961sneets-sheet 2 4d a Pere IN VEN TOR #ara/d 0 Marr/s.

FIE E fam/0g United safes Pat-em o 3,176,5l8 DUAL ACCELERATUN RANGEENTEGRATING ACCELERMETER Harold D. Morris, Grinda, and Walace E. Hyde,dr.,

Moraga, Calif., assignors to Systran-Donner Corporation, Concord,Calif., a corporation of California Filed Aug. 24, i961, Ser. No.133,701 16 Claims. (Cl. 73-5tl3) This invention relates to anintegrating accelerometer and more particularly to a dual accelerationrange integrating accelerometer.

ln certain missile applications, it is desirable to provide a separationmonitor which is capable of sensing the additional velocity which isimparted to the missile after the flight programmer has terminated thethrust from the booster and separated the booster from the missile. Inother missile applications,l it is desirable to control the velocity ofa missile in accordance with a predetermined command velocity so thatthe missile will arrive at the final landing point with optimumaccuracy. Devices suitable for such a purpose have heretofore not beenavailable, and for that reason there is a need for such devices.

In general, it is an objectof the present invention to provide a dualacceleration range integrating accelerometer which will perform thefunctions set forth above.

Another object of the invention is to provide an inegratingaccelerometer of the above character which will measure the time betweenthe command to terminate the thrust and the time the thrust isterminated and the velocity increment added during this period ofpowered Hight. t

Another object of the invention is to provide an integratingaccelerometer of the above character which will measure the velocityincrement added because of other forces.

Another object o the invention is to provide an integratingaccelerometer of the above character in which can be-utilized forpowering a missile at a commanded velocity.

high accuracy is obtainable.

Another object of the invention is to provide an in.- tegratingaccelerometer of the above character which recycles itself.

Another object of the invention is to provide an integratingaccelerometer of the above character which has very low switching times.

Another object of the invention is to provide an integratingaccelerometer of the above character which has a digital memory.

Another object of the invention is to provide an integratingaccelerometer of the above character which Another object of theinvention is to providel an in- Y tegrating accelerometer of the abovecharacter in which a control signal is developed which indicates whetherthe missile is iiying above or below the commanded velocity.

Another object of the 'invention is to provide an integratingaccelerometer of the Aabove character vwhich is utilized for controllingthe thrust applied to a missile.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiments are set forthin detail in conjunction with the accompanying drawings.

Referring to the drawings:

FIGURE l is a block diagram of a dual'acceleration range integratingaccelerometer incorporating our invention.

FEGURE 2 is a block diagram of another embodiment of our dualacceleration range integrating accelerometer.

In general, our dual range integrating accelerometer con- Ice sists of apair Vof accelerometers', one of which is used for measuring high trustand the other of which is used for measuring low thrust. Velocityintegrating means is adapted to be connected to eitherof theaccelerometers under the control of comparator means which senses whenthe thrust is within the range of one of the accelerometers.

in FIGURE l, we have shown a block diagram of a dual acceleration rangeintegrating accelerometer incorporating our invention which, a shown,consists of a high G accelerometer lil and a low G accelerometer 12. Theaccelerometers 1i and 12 can be of any suitable type such as thatdisclosed in copending application Serial No. 794,487 led February 4,1959. The .outputs of the accelerometers 11 and 12 are connected tocontacts l and 3 of a relay RYl kthrough resistors 13 andy i4. Themovable contact 2 of the relay RY1 is connected to a velocity integratori6 which consists of an ampliiier V17 and an integrating capacitor 18connected across the input and output terminals of the amplifier. Theoutput of the velocity integrator is connected to a control amplifier i9through a resistor 21. The control amplifier consists of an amplifier 22and a feedback resistor 215 connected between the input and outputterminals of the amplifier. The output of the control amplifier l? isconnected to an electrically operated hydraulic control valve 26 througha resistor 27.`

The control mnplilier is provided with a negative reference. from acommand line 31 which is connected to the amplier through a resistor 32;The reference is supplied to the command line 31 from a reference supply34 which is connected through a potentiometer 36 to ground; The wiper 37of the potentiometer is connected to the command line and makes itpossible to apply a reference of diierent values to the command line toprovide a command velocity as hereinafter described.

Means is provided for automatically transferring from the high Gaccelerometer to the low G accelerrometer when the thrust oracceleration comes within the range of the low G accelerometer andconsists of a comparator which senses'when thelowG 'accelerometer comesout of saturation and operates relay RY at this time.

Operation of the dual acceleration range integrating accelerometer shownin FGURE 1 may now be'briey described. Let it be assumed that theintegrating accelerometer shown in FIGURE .l is to be used as a zoningunit for a small missile. Also let it vbe assumed that the missile is ofa type which has a sustainer engine as well as a main booster engine andthat the control device is a control valve for operating the sustainerengine. Also let it be assumed that it is desired that the missile flyon a vacuum trajectory, that is, assuming that there is no air. This isaccomplished by adjusting the thrust of the engine `so -tha't it isequal to the drag of the air on the nose of the missile. The vacuumtrajectory determines the range of the missile and makes it possible todetermine the landing place-of themissile very accurately. Y 'f Y .pUpon ring of the missile, the `high G accelerometer 1i measures the mainthrust of the booster may be very high, as for example, 8O Gs.Thismeas'ured thrust is applied through the contacst` 1 and 2 of ,therelay RY?. to the velocity integrator, lo. As the booster for themissile ,burns out, the acceleration of the missile decreases vandfinally reaches a value at which the saturation sensing comparator 4ioperates the relay RYl to closev contacts 2 and 3. This low Gaccelerometer can measure any suitable value of acceleration,l as kforexample, acceleration from zero to 3 G. This acceleration informationfrom the ilow G accelerometer 12 isalso applied to the velocityintegrator and is supplied 'to the control amplier 19 to operate thecontrol device 26 in accordance with the command which is applied to thecontrol amplifier 19.

- The command velocity which is applied to the control ampliiier 19 iscalculated in such a manner thatit represents the true velocity of themissile excluding the eiiect of gravity. Thus, the command signal on theline 31 is a reference which is proportional to the command velocity. Anerror signal is generated by the control amplifier, 19 which isdetermined by the difference between the signal applied to the controlamplifier 19 from the velocity integrator 16 and the signal applied onthe line 31 to control the valve 26. This valve, in turn, regulates thesustainer engine to cause the missile to fly at the commanded velocitythroughout its entire flight.

Although not shown, the control amplifier 19 is provided with means toprevent saturation during the iirst interval of ,ight when the missileis below the desired velocity. This is a voltage operated resistor whichis represented by the resistor 23. If it is desired to provide dampingforthe system, an acceleration signal can be fed directly from aresistor (not shown) in series with the capacitor 18 of the velocityintegrator to provide stable overall operation. The system shown is aclosed loop servo from the engine to the accelerometer which senses theengine thrust through the integratorreading velocity to thecontrolamplifier back to the hydraulic valve 26 controlling the engine.

Another embodiment of our invention is shown in PIG- URE 2 and consistsof a high G accelerometer 51 and low G accelerometer 52. Theaccelerometers 51 and 52 can be of a suitable type such as the Model4310 accelerometer manufactured by the Donner Scientific Division ofSystron-Donner Corp. The accelerometers may have any suitablerange. Forexample, the high G accelerometer can have a range of i 40 G whereas thelow G accelerometer can have a range of il G. The high. C accelerometer51 is provided with a nulling circuit which is necessary to obtain thepropertransient response from the high G accelerometer. This nullingcircuit or loop consists of the windings 53 of the accelerometer whichis connected to a nulling integrator 54 consisting of an amplifier 56and an integrating capacitor 57. The nulling integrator is connectedthrough a resistor 58 to a normally closed (indicated by the crosssectioning) switch 59 to the other side of the winding 53 to provide aclosed loop. This nulling loop serves to suppress the output of the highG accelerometer to zero prior to when the thrust termination isreceived. The nulling loop is connected to ground through a resistor 61which. serves as load resistor.

The outputfof the high G accelerometer is connected to another normallyopen electronic switch 62 which is connected to contact 3 of relay YRYZ.

The low G accelerometer 52 is provided with a winding 64, one end ofwhich is connected to ground through a resistor 66. The same end of thewinding 64 is connected to contact 6 of relay RY2 through resistor 67and trim resistor 68. Movable contact 2 4of relay RY2 is connected toVground through a load resistor 71. `As hereinafter explained thisresistor 71 serves as an alternate load for the high G accelerometer.Stationary contacts 1 and 6 of relay RY2 are interconnected by conductor72. Movable contact of relay RY2 is connected through contacts 1 and 2of relay RY3 to a total information integrator 74. The total informationintegrator consists of an ampliiier 76 and an integrating capacitor 77.The operation of the totalinformation integrator is controlled by anormally closed electronic Yswitch 78. The output` of theV totalinformation integrator is supplied to a voltage divider network whichsupplies information to terminal G to provide total information in asuitable quantity such as feet per second. In a similar manner, the lowG accelerometer is connectedto a railing information integratorv 86through contacts 3 and4 of relay RY3 and 4 through resistors 87 and 88to one end of the winding 64 of the acceleroriieterl 52. The voltagedivider network 81 consists of resistors 82 and 83 and a trim resistor84.

The tailing information integrator 86 consists of an amplifier 89 and anintegrating capacitor 91. A normally closed electronic switch 92 isprovided for controlling the operation of the integrator 86. The outputof the integrator is supplied to voltage divider network 93 consistingof resistors 94 and 96. The output from the voltage divider is suppliedto terminal H in the form of tailing information in a suitable quantityas feet per second.

The electronic switch 59 and the electronic switch 78 are controlled bya switch control flip-flop or bistable circuit 101 and are connected tothe bistable circuit 101 as shown. The other side of the switch controliip-flcp 101 is connected to the normally open electronic switch 62.Another switch control iiip-iiop 102 is provided for controlling theelectronic switch 92. The switch control flip-Hops 101 and 102 areprovided with two sides and one side is cross-sectioned to show whichside is normally on. The electronic switches are cross-sectioned toindicate a normally closed position and are left blank to indicate anormally open position.

The output of the high G accelerometer 51 is connected to a comparator104 which is provided for the purpose of determining when theacceleration drops a predetermined acceleration range. The low Gaccelerometer 52 has its output also connected to` a comparator 10Swhich is used for determining when the thrust being measured by the lowG accelerometer comes within the acceleration range of the low Gaccelerometer.

A control and timing circuit is provided which includes a trigger gate106 to which the terminal B is connected through al1-C. blockingcapacitor 107. The compute commands are supplied to the B terminal tocommence the operation of the circuitry as hereinafter described. Thetrigger gate 106 is a conventional bistable circuit and has its outputapplied to a pair of diodes 108 which serve the purpose of isolating andselecting the positivegoing transient from each change of stateof thebistable circuit. The common output fromy the diodes 108 is connected toan initiate flip-Hop 109 which holds the compute command as hereinafterdescribed. The output of the initiate flip-nop is connected to theswitch control iiip-tiop 101 through a coupling capacitor 111. It isalso connected to one input of an AND gate 112. The other input of theAND gate is connected to the comparator 105. The output of the AND gate112 is connected to one side of the switch control flip-flop 1 02. Theinitiate ip-iiop 109 is also connected to three time delay devices 114,and 116. Each is set up after a predetermined time interval, as forexample, time delay device 114 can be set to operate after -.05 second,time delay device 115 after 2.5 seconds, and automatic reset delaydevice after 22.5 seconds.` The output of the time. delay device 114 isconnected to relay RYZ which is provided with two windings RYZA andRYZB. Time delay device 115 is connected to the windings RYSA and RYSBof the relay RY3. Time delay device, 116 is connected to any automaticreset line 117 which is connected to a recycle delay device 118 which.is connected through a coupling capacitor 119-to the trigger gate 106.

Y The rinitiate Hip-flop 109 is also connected to one of the inputs ofan AND gate 119. The other input of the AND gate 119 ispconnected to thecomparator 104. The output of the AND gate 119 is connected to one inputof an OR gate 121. The other input of the OR gate is connected to a stop matrix 122; The output of the OR gate 121 is connected to a digitaltimer control ip-tiop 123. The digital timer control iiip-flop also hasits input directly connected to the initiate iiip-flop 109. The outputof the digital timer Ycontrol flipflop 123 is connected to a digitaltimer oscillator 124 which is connected to a digital timer 126. The stopmatrix 122 is connected to the digital timer 126. The

digital timer 126 is connected to a digital to analog converter 127. Theoutput of the digital to analog converter is supplied to an outputterminal I.

Means is provided for resetting the circuitry when the reset command isapplied to the reset terminal C and consists of a reset line 131 whichis connected to the trigger gate 166 and to one of the inputs of an ORgate 132. The other input of the OR gate 132 is connected to the resetline 117. The output of the OR gate 132 is connected tothe switchcontrol flip-tiops lill and 102. The reset line 131 is also connected toanother OR gate 133 and the other input of the OR Agate 133 is connectedto the initiate flip-flop 109. The output of the OR gate 133 isconnected through a coupling capacitor 134 to the digital timer 126.

Operation of the circuitry of the block diagram shown in FIGURE 2 maynow be briefly described as follows. Let it be assumed that thecircuitry shown in the block diagram is being utilized as a separationmonitor to sense the additional velocity which is imparted to a missileafterthe flight program computer had entered a command to terminate thethrust of the main booster being utilized. i

Upon receipt of the thrust termination command from the guidancecomputer at the terminal B, the bistable circuit ltd will flip toproduce an output which, in turn, will cause the bistable circuit 199 toflip. This will cause operation of the switch control flip-tiop 1511.

When the switch control hip-flop 161 operates, it opens the normallyclosed electronic switch 59 to disconnect the nulling integrator Vfromthe high G accelerometer 51. At the same time, the electronic switch 62is closed by the operation of the switch control flip-hop 161 so thatthe output from the high G accelerometer is applied to the totalinformation integrator 74. It should be pointed out that the loadresistor 61 is equal to the input resistor 63. Resistor 71 for the highG accelerometer is equal to the input resistor 63 and the load resistor61. At the same time that the electronic switch 62 is closed, the switch78 is opened to permit operation of the total information integrator'71%.L

Thus, at time zero, when the thrust termination command arrives, theoutput from the high G accelerometer. S1 is applied to the totalinformation integrator 74 to determine the amount of velocity added tothe missile during the time between the command to terminate thrust andthe time when the thrust termination of the main booster engine actuallybecomes effective.

From the foregoing, it will be seen that the total informationintegrator 74 will record the total velocity increment applied to themissile after time zero until the i'lnal termination of integration at apredetermined time interval, that is, for example, 21/2 seconds later.However, the circuitry is arranged in such a manner that the totalinformation integrator will only receive information from the high Gaccelerometer for a predetermined period of time, as for example, 50milliseconds, after which the time delay circuit 114 causes energizationof relay RYZ to switch the input terminal of the total informationintegrator 74 to the low G accelerometer 52. This is done because thelow G accelerometer has less drift and zero uncertainty and is,therefore, more suitable for measuring low levels of acceleration whichwill normally occur at this time. Thereafter, the acceleration measuredby the low G accelerometer is applied to the total informationintegrator 74.

Nhen the total thrust being measured by the high G accelerometerdecreases below a predetermined value, as for example, 0.95 G, thecomparator 11M supplies a signal to the AND gate 119. Assuming there isa signal from the initiate flip-flop 169, there will be an output fromthe AND gate 199 to the OR gate 121 to cause operation of the digitaltimer control flip-flop 123 to stop the operation of the digital timeroscillator 124 which was started by the compute command transmittedthrough gate 1% and initiate flip-hop 139 to prevent it from supplyingclock pulses to the digital timer 12o. This serves as a measurel of thetime delay between the time the flight program computer commands athrust termination and the time that the command actually was madeeffective by the thrust dropping down below the thrust for which thecomparator 104 is set.

When the low G accelerometer 52 comes out of saturation, the comparator10S is operated to supply a signal to the AND gate 112. Assuming thatthere is a signal from the initiate iiip-iiop 1tl9, the switch controltiip-op 1152 will be operated to open the normally closed electronicswitch 92 to permit operation of the tailing information integrator 36to thereby permit this integrator to record the Velocity increment.

Electronic switches in the form of semiconductor devices are utilized inthis application because it is undesirable to lose any velocityinformation during the switching. For that reason, relays normally wouldnot be satisfactory for such high speed operation.

After the end of the time interval for which the time delay device isset, the relay RYE is energized to open its contacts to prevent theapplication of additional information to the integrators 7d and 86.Thus, after the time delay device 115 is set, no more information isapplied to the integrators 7d and 86.

In summary, it can be seen that the total information integrator 74records the total additional Velocity applied to the missile afterreceipt of the command to terminate thrust. The tailing informationintegrator supplies the velocity increment applied to the missile objectafter the acceleration has dropped below a predetermined value, as

for example, below l G. The timing circuitry which in-V cludes the stopmatrix 122, the digital timer 126 and the digital analog converter'127records the time delay from the initiate to the cessation of thrust yandt-o remember it for a predetermined period, as for example, 20 seconds.Since the ratio of record time to the integrating or record time isrelatively large, a digital system is usedV for accurate measurement oftime and is held in a digital form. The other outputs are held in ananalog form.

It is apparent'from the foregoing that we have pro-v vided a dualacceleration range integrating accelerometer which has mmy applications.It is relatively simple and inexpensive toV manufacture.

We claim:

1. In a dual acceleration range integrating accelerometer, a iirstaccelerometer having a relatively high acceleration range, a secondaccelerometer having a relatively low acceleration range, .a millingloop connected to said iirst accelerometer to maintain the output atnull until apredetermined time interval elapses, integrating means,comparator means connected to one of said accelerometers for determiningwhen the acceleration being measured is within the range of said oneaccelerometer and switching means connected to said comparator means andoperated by said comparator means for applying the `output of one ofsaid accelerometersy to said integrating means.

2. In av dual acceleration range integrating accelerometer forcontrolling a sustainer engine on a missile, a first accelerometerhaving a relatively high acceleration range, a second accelerometerhaving a relatively low acceleration Y range, an integrator, switchmeans connecting the rst and second Vaccelerometers to the integrator,means for determining when the acceleration being measured comes Withinthe range of the second accelerometer to operate said Vswitching meansto disconnect the tirst accelerometer from the integrator and connectthe second accelerometer to the integrator, a control amplifierconnected to the output of the integrator, means for supplying anegative reference tothe input of the control amplifier and controlmeans connected to the output of the control amplifier for con- Y.trolling the sustainer engine to maintain a substantially constantcommand velocity for the remainder of the ilight as determined by thecontrol amplifier.

3. In a dual acceleration range integrating accelerometer, a iirstaccelerometer having a relatively highaccelera-V tion range, a secondaccelerometer having a relatively low acceleration range, a totalinformation integrator, a partial information integrator, `switch meansconnecting the first and second accelerometers to the total informationintegrator, switch means connecting the second accelerometer to thepartial information integrator, means for nulling the output of the rstaccelerometer before receipt of a compute command, each of saidintegrators including switch means for preventing operation of the same,means for operating the switch means of the total information integratorso that the total information integrator commences to operate upon thereceipt of the compute command, time delay means connected to saidswitch means connected to said first and second accelerometers forprogramming the operation of the same, said time delay means commencingoperation upon receipt of the compute command, and means for sensingwhen the acceleration being measured comes within the range of thesecond accelerometer for commencing operation of said'V partialintegrator.

4. An accelerometer as in claim 3 wherein said switch means connected tothe iirst and second accelerometers includes a pair of relays, whereinsaid time delay means includes at least a pair of time delay devices andwherein the irst time delay device determines the period of timeduring'which the iirst accelerometer measures acceleration and thesecond time delay device determines the period` of time during which thesecond accelerometer measures acceleration. A

5. An accelerometer as in claim 3 together with time measuring means formeasuring the time between the receipt of the compute command and thetime acceleration falls below a predetermined level.

6. An accelerometer as in claim 5 wherein said time measuring meansincludes a digital timer, a digital timer oscillator connected to adigital timer, a digital timer control ip-ilop connected to the digitaltimer oscillator and a digital-to-analog converter. connected to thedigital timer.

7. In a dual acceleration range integrating accelerometer, a iirst.accelerometer having a relatively high acceleration range, a secondaccelerometer having a relatively low acceleration range, integratormeans, switching means for selectively connecting said iirst and secondaccelerorneters to said integrating means, and means connected to saidswitching means for sensing when the acceleration being measuredcomeswithin the range `of the second accelerometerfor operating saidswitching means to disconnect said iirst accelerorneter from saidintegrator means and to connect said second accelerometer to saidintegrator means, said integrator means consisting of a totalinformation integrator adapted to be connected by said switching meansAto said tirst accelerometer and a partial information integrator adaptedto be connected to said second accelerometer by said switching means.

8. An accelerometer as in claim 2 together with means to preventsaturation of the control amplifier during the first interval of iiightwhen the missile is below the desired velocity.

9. In apparatus of the character described, an accelerometer having apendulous mass and an analog output, a nulling loop connected to theelectrical output of the accelerometer for maintaining the pendulousmass of the accelerometer continuously at its electrical null for apredetermined period of time, said nulling loop including switch meanscapable of assuming open and closed conditions, and means forcontrolling the operation of said switch means.

l0. Apparatus as in claim 9 wherein said nulling loop includes anintegrator.

References Cited by the Examiner` UNITED STATES PATENTS 2,207,908 7/40Beecher 73-197 2,603,726 7/52 McLean 73-503 2,613,071 10/52 Hansel73-490 2,943,393 7/60 Bosch 73-516 2,970,479 2/61 Wikstrorn 73-5142,980,894 4/61 Lindemann 73-197 3,073,550 l/63 Young 244-14 FOREIGNPATENTS 779,156 7/57 Great Britain.-

VRICHARD C. QUEISSER, Primary Examiner.

S. LEVINE, ROBERT L. EVANS, JAMES I. GILL,

Examiners.

3. IN A DUAL ACCELERATION RANGE INTEGRATING ACCELEROMETER, A FIRSTACCELEROMETER HAVING A RELATIVELY HIGH ACCELERATION RANGE, A SECONDACCELEROMETER HAVING A RELATIVELY LOW ACCELERATION RANGE, A TOTALINFORMATION INTEGRATOR, A PARTIAL INFORMATION INTEGRATOR, SWITCH MEANSCONNECTING THE FIRST AND SECOND ACCELEROMETERS TO THE TOTAL INFORMATIONINTEGRATOR, SWITCH MEANS CONNECTING THE SECOND ACCELEROMETER TO THEPARTIAL INFORMATION INTEGRATOR, MEANS FOR NULLING THE OUTPUT OF THEFIRST ACCELERATOR BEFORE RECEIPT OF A COMPUTER COMMAND, EACH OF SAIDINTEGRATORS INCLUDING SWITCH MEANS FOR PREVENTING OPERATION OF THE SAME,MEANS FOR OPERATING THE SWITCH MEANS OF THE TOTAL INFORMATION INTEGRATORSO THAT THE TOTAL INFORMATION INTEGRATOR COMMENCES TO OPERATE UPON THERECEIPT OF THE COMPUTE COMMAND, TIME DELAY MEANS CONNECTED TO SAIDSWITCH MEANS CONNECTED TO SAID FIRST AND SECOND ACCELEROMETERS FORPROGRAMMING THE OPERATION OF THE SAME, SAID TIME DELAY MEANS COMMENCINGOPERATION UPON RECEIPT OF THE COMPUTE COMMAND, AND MEANS FOR SENSINGWHEN THE ACCELERATION BEING MEASURED COMES WITHIN THE RANGE OF THESECOND ACCELEROMETER FOR COMMENCING OPERATION OF SAID PARTIALINTEGRATOR.